1. Field of the Invention
The present invention relates generally to control valve systems, and particularly to a shut-off valve testing system for testing and operating the main shutdown valve that controls gas flow in a refinery, industrial plant or other facility.
2. Description of the Related Art
In the oil, gas, petroleum and power industries, natural gas or other combustible gas is often used to provide the required heat or combustion motive power for many operations in a processing refinery, plant, or other industrial facility. Various conditions may occur that necessitate immediate shut down of the operations of the facility. In those facilities, a majority of the final control elements of a shutdown system are implemented with fast acting shut-off valves. In such industries, a majority of the shut-off valves remain open while the operation is operating safely in a nominal controlled state. Such shut-off valves are closed only upon actuation of the shutdown system of the facility, arising from an out-of-control process or during a normal maintenance outage.
In practice, the testing of emergency shut-off valves is normally done during shut down of the facility operation. However, there is a tendency for such valves to stick or freeze due to corrosion or other reasons, which may lead to an unsafe condition where the valve cannot be closed during an emergency shutdown. This problem is exacerbated by economic conditions in the operation of the facility that have lead to a reduction in the frequency of valve shut-offs for maintenance or testing purposes. For example, some operations may run continuously for one or more years without shutting down the operation for maintenance.
State of the art emergency shut-off systems that control the shut-off valves have a number of features to detect system failures, and typically include redundancies for added reliability. However, such systems may not provide for the testing of a shut-off valve, other than by operating the valve through its normal stroke or travel. The problem is that operating the valve through its full stroke or travel, i.e., completely closing the valve, causes an undesirable disruption in the operation of the facility.
Thus, a shut-off valve testing system solving the aforementioned problems is desired.